1. Field of the Invention
The present invention relates to a vehicle control device making a control of an automatic transmission and, more particularly, to a gear ratio control at the time of turning.
2. Description of the Related Arts
A vehicle control device of such type has been conventionally known, and in which turning of a vehicle is detected and a gear ratio is made larger during turn (it is changed to the shift-down side), whereby a vehicle is brought in speed reduction due to generation of an engine brake and the turn is made safely, as well as an accelerating performance at the end of the turn is improved (refer to the Japanese Patent Publication (unexamined) No. 169330/1985 and the Japanese Patent No. 3588818).
In the above conventional vehicle control device, to detect the turn of a vehicle, a steering wheel angle sensor, a yaw rate sensor or a lateral acceleration sensor has been used. In the steering wheel angle sensor, however, a driver generates a steering torque, this torque exceeds the friction of a steering mechanism, and then at the time point when the steering wheel begins to rotate, it is eventually detected to be turning. In the yaw rate sensor and the lateral acceleration sensor, a wheel is steered in accordance with the rotation of the steering wheel, a lateral force is generated at a tire, and then at the time point when the movement of a vehicle in the yaw direction and in the lateral direction is generated, it is eventually detected to be turning. Accordingly, in the conventional vehicle control device, the turning is eventually detected after going through several stages since a driver intends to turn and generates a steering torque.
On the other hand, in the case of making a gear ratio change for turning, it is ideal to complete the gear ratio change before a vehicle begins to turn because there is no change in driving force during turning and thus an uncomfortable feeling is not brought to a driver. Therefore, in such device, it is important to detect the turn intention of a driver and to start the change of gear ratio as early as possible. As described above, however, since detection timing of the turn is late in the conventional device, a problem exists in that a driver is sometime provided with a sense of discomfort at the time of conducting the change of gear ratio. Moreover, the steering wheel angle sensor, yaw rate sensor and lateral acceleration sensor are very expensive, and another problem exists in bringing cost increase of the vehicle control device.